Interim Financial Statements - Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2018	Dec. 31, 2017
Income Taxes
Corporate tax rate (as a percent)		21.00%	35.00%
U.S. federal and state tax liability related to transition tax on repatriation of foreign earnings and profits	$ 52.2	$ 52.2
Amount of deemed repatriation of foreign earnings and profits	946.0	946.0
Income tax benefit related to remeasurement of deferred tax assets and liabilities due to change in enacted tax rate		301.2
Adjustments to provisional estimates :
Federal and State Change Due to Repatriation	12.5
Other Adjustments	(0.9)
Total SAB 118 Benefit	$ 11.6
Provisional estimate, income tax benefit from enactment of the Act		243.4
Income tax benefit from enactment of the Act		$ 255.0